roller rockers vs contact tip rockers

[BILL-C]

Why would anyone assume that the ideal rocker pad shape is symetrical on opening and closing sides? It's actually pear shaped.

[cjperformance]

Why would anyone assume that the ideal rocker pad shape is symetrical on opening and closing sides? It's actually pear shaped.

I dont know, some just dont get it.

[Walter R. Malik]

As the valve opens & closes via rocker action, the distance from the valve tip to the trunnion centre changes. It can get larger &/or smaller depending on the geometry, but it WILL the distance will change. The rocker tip moves in an arc; the valve does NOT.

Sorry, you are incorrect. Experiment with tip profiles and you will see what we mean!

Yes ... some people will never understand but, they will argue till the end of time.
Roller rockers came into being because they are more forgiving to bad geometry.
The contact distance with a non roller tip rocker arm does and is supposed to change which minimizes scrubbing; from the inside of the valve tip to the outside of the valve tip IS a greater distance from the fulcrum. It does not change much ratio because the pushrod angularity changes the line actuating distance from the fulcrum, also.
If it does not act that way then the geometry is not near correct.

[swampbuggy]

Which one is the one who don't get it where is Warp with some input ???

[Tuner]

When the geometry is right the ball and socket rocker rolls across the stem tip and slides on the ball.

Five pages and not one mention of the carbon paper or ZigZag rolling paper test to determine if the rocker pad or roller is rolling or sliding ... ?? Where's the geezers, what's wrong with you guys?

[cjperformance]

When the geometry is right the ball and socket rocker rolls across the stem tip and slides on the ball.

Five pages and not one mention of the carbon paper or ZigZag rolling paper test to determine if the rocker pad or roller is rolling or sliding ... ?? Where's the geezers, what's wrong with you guys?

Yes, 'ball and socket' type and plain radius rocker ends (as used for many valve tip end adjustable rockers) will always sweep the valve tip.
I find brass shim stock the best , .005"/.010" shim stock between the rocker and the valve tip very clearly shows up what sweep or roll pattern you have.

[swampbuggy]

One of the guys at T and D told me lipstick works good that was about 1998, also have been told sharpie color the valve tip ???

[Geoff2]

Craig,
[ and some others ]

You are still not getting it. But you did mention the magic word, so maybe you will get it. The magic word being: arc. The rocker tip rolls/sweeps/ slides, [ take your pick, all mean the same for this scenario ], in an arc, across the valve tip. If it is a roller tip, it rolls across the valve tip. If it is non roller tip, it slides across the valve tip. The amount that the rocker tip slides is going to vary on the geometry, but there WILL be some sliding motion. If there is no sliding motion as you, McClain & others claim, there would be no need for a roller tip on a rocker because according to your theory, there is point contact only; so just a very narrow steel pad could be used saving money & making a reliable rocker with less parts to fail!! ...... But of course they are not made like that for very good reasons.....

The rocker at max valve lift demonstrates the action better than anything: the distance from the trunnion centre to the contact point is at it's greatest at max valve lift. As the valve closes, this distance reduces. With a roller tip rocker, there is less movement across the valve tip [ but always some movement ] & more with a non-roller tip.

Finally,
Are these people wrong also:

[1] "As the rocker moves to mid travel, the [ roller ] tip moves off the centerline." Reher-Morrison engine assy

[2] "As the valve opens, the rocker contact point moves across the valve tip". How to build HP, Vol 1. D.Vizard

[BILL-C]

For a roller tip rocker, the distance from trunion to roller tip is fixed. On a stock rocker , that contact point to pivot distance changes with lift. That explains the large wear pattern on old , non blueprinted rockers, and the variable rocker ratio that results.

[DaveMcLain]

Craig,
[ and some others ]

You are still not getting it. But you did mention the magic word, so maybe you will get it. The magic word being: arc. The rocker tip rolls/sweeps/ slides, [ take your pick, all mean the same for this scenario ], in an arc, across the valve tip. If it is a roller tip, it rolls across the valve tip. If it is non roller tip, it slides across the valve tip. The amount that the rocker tip slides is going to vary on the geometry, but there WILL be some sliding motion. If there is no sliding motion as you, McClain & others claim, there would be no need for a roller tip on a rocker because according to your theory, there is point contact only; so just a very narrow steel pad could be used saving money & making a reliable rocker with less parts to fail!! ...... But of course they are not made like that for very good reasons.....

The rocker at max valve lift demonstrates the action better than anything: the distance from the trunnion centre to the contact point is at it's greatest at max valve lift. As the valve closes, this distance reduces. With a roller tip rocker, there is less movement across the valve tip [ but always some movement ] & more with a non-roller tip.

Finally,
Are these people wrong also:

[1] "As the rocker moves to mid travel, the [ roller ] tip moves off the centerline." Reher-Morrison engine assy

[2] "As the valve opens, the rocker contact point moves across the valve tip". How to build HP, Vol 1. D.Vizard

They are not wrong in that the contact point moves on the tip of the valve BUT you are wrong in thinking that this requires a sliding action to make happen. It does not as long as the rocker arm is set up with the right geometry and the correct arc on the tip.

[strokersix]

This discussion reminds me of an often heard myth about involute gearing that the mating teeth roll against each other and there is no sliding. This is false. The only point where there is no sliding is when the tooth contact is directly between shaft centers. Everywhere else there is sliding as the teeth enter and exit the mesh.

This rocker geometry discussion I think is very similar. I believe there will always be sliding of some magnitude. The large contact radius effectively increases bearing area thereby reducing friction and wear but there is still sliding. In fact, some sliding is probably preferable to improve lubrication of the interface.

[strokersix]

A thought experiment:

Let's say the width of the contact witness mark on the valve tip is 1/8 inch and the corresponding witness mark on the rocker tip is 1/2 inch. (made up numbers for example only). The only way to generate unequal width witness marks is for there to be sliding involved. In this case 1/2 - 1/8 there was at least 3/8 inch sliding.

Witness marks on rocker tips are larger than on valve tips in my observation.

[MadBill]

Observing/inspecting one or more specific rocker arm's action and seeing evidence of slippage would not be proof that non-slip contact was not possible. I'm sure though if I'd scored way more on my Grade 12 Geometry final sixty years ago I could work it out one way or the other...

[Geoff2]

Dave Mc,
A roller tip rocker rolls across the valve tip. I don't think there is any dispute about that.
However, a rocker with a pad, such as stock rocker, slides across the valve tip & the best geometry in the world isn't going to change that. We see that with worn rockers that show a WIDE wear mark on the rocker pad. What you are forgetting is that as the rocker moves up & down, the tip swings in & out on an arc, moving closer to, & way from, the valve tip. If the valve tip moved in the same arc, there would be no sliding....but it doesn't move in an arc.

Bill-C.
Yes the trunnion to roller tip distance is fixed. A popular misconception is that this distance forms part of the rocker ratio. It doesn't. The ratio is from the trunnion centre to where the tip makes contact on the valve tip & will change through the rocker travel.

[swampbuggy]

Bill. I think i might have just figured out your age lol. Mark .